Such an apparatus is used to position a work spindle in predetermined angular relationship to a tool in order that a machining operation may be carried out on a workpiece carried by the spindle. For example it may be required to carry out a drilling operation on a workpiece, in a direction which is transverse with respect to the axis of the work spindle. For this purpose, it is necessary to ensure that the work spindle will not rotate from the required position about the spindle axis and also that it is correctly aligned with respect to the tool so as to produce the desired position of the hole to be drilled. Angular orientation of the work spindle may also be required for automatic loading of shaped workpieces.
This angular movement has, in the past, been achieved in one example by the use of a cam whereby the work spindle can be rotated, the cam having a recess, corresponding with the predetermined position, in which a cam follower will locate. This arrangement tends to be somewhat inflexible as well as having other disadvantages.